The present invention relates in general to radio frequency receiver technology and more particularly to a two stage low noise amplifier.
In radio frequency receiver topologies, radio frequency filters provide outputs which are single ended. However, typical receiver implementations require differential signals in order to take advantage of isolation benefits. In order to obtain differential signals though, current radio receiver implementations use off chip balun circuits which increases the cost for the receiver. Also, effective receivers need to have frequency trimming and image rejection capabilities. Therefore, it is desirable to have a receiver circuit that can provide the necessary capabilities in a more effective manner.
From the foregoing, it may be appreciated by those skilled in the art that a need has arisen for a receiver circuit that can perform single to differential conversion with frequency tuning and image rejection functions. In accordance with the present invention, a two stage low noise amplifier circuit is provided that substantially eliminates or reduces disadvantages and problems associated with conventional receiver implementations.
According to an embodiment of the present invention, there is provided a two stage low noise amplifier that includes a first stage performing single to differential conversion of an input signal. Since the load is tuned, some image rejection is achieved in the first stage. A second stage receives a differential signal from the first stage. The second stage performs differential tuning of a center operating frequency in order to provide image rejection of the differential signal.
The present invention provides various technical advantages over conventional receiver implementations. For example, one technical advantage is to provide single to differential conversion, frequency tuning, and image rejection in an amplifier circuit design on a single semiconductor device. Another technical advantage is to eliminate a need for A.C. coupling and D.C. bias level shifting between stages of an amplifier circuit design. Yet another technical advantage is to provide single to differential conversion without a loss in amplifier gain. Other technical advantages may be readily apparent to those skilled in the art from the following figures, description, and claims.